Fiber channel port by-pass selector section for dual ported disk drives

ABSTRACT

A data storage system having a plurality of disk drives. Each one has a pair of bi-directional ports. A pair of directors controls the flow of data to and from the disk drives. A first fiber channel port by-pass selector section is provided. The first fiber channel by-pass selector section includes: an input/output port coupled to a first one of the directors; and, a plurality of output/input ports connected between a first one of the ports of the plurality of disk drives through a first plurality of fiber channel links. The first fiber channel port by-pass selector section is adapted to couple the first one of the directors serially to one, or ones, of the first ports of the plurality of disk drives through a first fiber channel selectively in accordance with a control signal fed to the first fiber channel by-pass selector section. The first fiber channel includes one, or more, of the first plurality of fiber channel links. A second fiber channel port by-pass selector section is provided having an input/output port coupled to a second one of the directors and a plurality of output/ports serially connected between a second one of the pair of ports of the plurality of disk drives through a second plurality of fiber channel links. The second fiber channel port by-pass selector section is adapted to couple the second one of the directors serially to one, or ones, of the second ports of the plurality of disk drives through a second fiber channel selectively in accordance with the control signal. The second fiber channel includes one, or more, of the second plurality of fiber channel links.

BACKGROUND OF THE INVENTION

This invention relates generally to data storage systems and more particularly to data storage systems having a plurality of magnetic storage disk drives in a redundancy arrangement whereby the disk drives are controllable by first disk controllers and second disk controllers. Still more particularly, the invention also relates to systems of such type wherein the disk drives are coupled to the disk controllers through a series, unidirectional, “ring” or, fibre channel protocol, communication system.

As is known in the art, in one type of data storage system, data is stored in a bank of magnetic storage disk drives. The disk drives, and their coupled interfaces, are arranged in sets, each set being controlled by a first disk controller and a second disk controller. More particularly, in order to enable the set of disk drives to operate in the event that there is a failure of the first disk controller, each set is also coupled to a second, or redundant disk controller. Therefore, if either the first or second disk controller fails, the set can be accessed by the other one of the disk controllers.

While today, most disk storage systems of this type use a Small Computer System Interconnection (SCSI) protocol, in order to operate with higher data rates, other protocols are being introduced. One higher data rate protocol is sometimes referred to as a fibre channel (FC) protocol. Such FC channel protocol uses a series, unidirectional, “ring” communication system. In order to provide for redundancy, that is, to enable use of the set of disk drives in the event that the first disk controller fails, as discussed above, the set is coupled to the second, or redundant disk controller, using a separate, independent, “ring”, or fibre channel communication protocol. Thus, two fibre channels are provided for each set of disk drives and their disk interfaces; a first fibre channel and a second fibre channel.

As is also known, when using the fibre channel communication protocol, if any element in the channel becomes inoperative, the entire channel becomes inoperative. That is, if the first disk controller becomes inoperative, or if any one of the disk drives in the set coupled to the first channel becomes inoperative (i.e., as where the disk interface fails, the disk interface is inoperative, or removed with its coupled disk drive, or where the disk drive coupled thereto fails, or is removed), the first fibre channel, is “broken”, or open, and becomes inoperative. The data stored in the entire portion of the set of disk drives coupled to the first disk channel is therefore unavailable until the inoperative first disk controller or inoperative disk drive is replaced. This is true with either the first channel or the second channel. One technique suggested to solve this problem is through the use of a switch, sometimes referred to as an LRC (i.e., a loop resiliency circuit) switch. Such LRC switch is used to remove an inoperative disk drive from its channel.

In one suggested arrangement, a printed circuit board is provided for each disk drive. The printed circuit board has a pair of LRCs, one for the first channel and one for the second channel. Thus, the open channel may be “closed” in the event of an inoperative disk drive by placing the LRC thereof in a by-pass condition. While such suggested technique solves the inoperative disk drive, or open channel problem, if one of the pair of LRCs fails, the entire printed circuit board having the pair of LRCs must be replaced thereby disrupting both the first and second channels; and, hence, disrupting the operation of the entire data storage system.

One technique suggested to solve this disruption problem requires n LRC switches (where n is the number of disk drives in the set) in the first channel, i.e., one LRC for each one of the n disk drives in the set and another n LRC switches in the second channel for each one of the n disk drives in the second channel. The first channel set of n LRCs is mounted on one printed circuit board and the second channel set of n LRCs is mounted on a different printed circuit board. A backplane is used to interconnect the two LRC printed circuit boards, the associated multiplexers, and the disk drives. In order to provide the requisite serial, or sequential, fibre channel connections, an elaborate, complex, fan-out wiring arrangement has been suggested for the backplane. Further, the slots provided for the two LRC boards eliminates two disk drives, and the disk interfaces which would otherwise be plugged into these two slots of the backplane.

Another fibre channel arrangement is described in U.S. Pat. No. 5,729,763 entitled “Data Storage System”, inventor Eli Leshem, issued Mar. 17, 1998, assigned to the same assignee as the present invention.

SUMMARY OF THE INVENTION

In accordance with one feature of the invention, a data storage system is provided having a plurality of disk drives. Each one has a pair of ports. A pair of directors is included for controlling the flow of information (i.e, data) to and from the disk drives. A first fibre channel port by-pass selector section is provided. The first fibre channel selector section includes: an input/output port coupled to a first one of the directors; and, a plurality of output/input ports connected between a first one of the ports of the plurality of disk drives through a first plurality of fibre channel links. The first fibre channel port by-pass selector section is adapted to couple the first one of the directors serially to one, or ones, of the first ports of the plurality of disk drives through a first fibre channel selectively in accordance with a control signal fed to the first fibre channel by-pass selector. The first fibre channel includes one, or more, of the first plurality of fibre channel links. A second fibre channel port by-pass selector section is provided having an input/output port coupled to a second one of the directors and a plurality of output/ports serially connected between a second one of the pair of ports of the plurality of disk drives through a second plurality of fibre channel links. The second fibre channel port by-pass selector section is adapted to couple the second one of the directors serially to one, or ones, of the second ports of the plurality of disk drives through a second fibre channel selectively in accordance with the control signal. The second fibre channel includes one, or more, of the second plurality of fibre channel links.

BRIEF DESCRIPTION OF THE DRAWING

These and other features of the invention will become more readily apparent from the follow detailed description when read together with the accompanying drawings, in which:

FIG. 1 is a block diagram of a data storage system according to the invention;

FIG. 2 is a block diagram of a redundant fibre channel network used in the system of FIG. 1 according to the invention;

FIG. 3 is a block diagram of a port by-pass section used in the redundant fibre channel network of FIG. 3 coupled to a bank of disk drives used in the system of FIG. 1 according to the invention;

FIGS. 4, 4A, and 4B are block diagrams of the system of FIG. 1 arranged in an expanded configuration according to the invention;

FIGS. 5, 5A and 5B are block diagrams of a redundant fibre channel network adapted for use in the system of FIG. 1 according to the invention;

FIGS. 5C-5G are diagrams of the network of FIGS. 5, 5A and 5B configured in a number of contracted configurations according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, a data storage system 10 is shown wherein a host computer 12 is coupled to a bank 14 of disk drives through a system interface 16. The system interface 16 includes a cache memory 18, having high memory address sections 18H and low address memory sections 18L. A plurality of directors 20 ₀-20 ₁₅. is provided for controlling data transfer between the host computer 12 and the bank 14 of disk drives as such data passes through the cache memory 18. A pair of high address busses TH, BH is electrically connected to the high address memory sections 18H. A pair of low address busses TL, BL electrically connected to the low address memory sections 18L. The cache memory 18 has a plurality of storage location addresses. Here, the storage locations having the higher addresses are in the high address memory sections 18H and the storage locations having the lower addresses are in the low address memory sections 18L. It should be noted that each one of the directors 20 ₀-20 ₁₅ is electrically connected to one of the pair of high address busses TH, PH and one of the pair of low address busses TL, BL. Thus, each one of the directors 20 ₀-20 ₁₅ is able to address all locations in the entire cache memory 18 (i.e., to both the high address memory sections 18H and the low address memory sections 18L) and is therefore able to store data in and retrieve data from any storage location in the entire cache memory 18.

More particularly, a rear-end portion of the directors, here directors 20 ₀-20 ₃ and 20 ₁₂-20 ₁₅, is electrically connected to the bank 14 of disk drives through fibre channel (FC) port by-pass sections 23 ₁-23 ₈ (described in more detail in connection with FIG. 3), respectively. and a front-end portion of the directors, here directors 20 ₄-20 ₁₁, is electrically connected to the host computer 12 through I/O adapter cards 22 ₁-22 ₈, respectively, as indicated. It should also be noted that each end of the busses TH, TL, BH, BL terminates in a pair of master and slave arbiters bus arbiters, not shown, as described in co-pending patent application Ser. No. 09/224,194 filed Dec. 30, 1998, entitled DATA STORAGE SYSTEM, inventor Mark Zani, assigned to the same assignee as the present invention, the entire subject matter thereof being incorporated herein by reference.

In operation, when the host computer 12 wishes to store data, the host computer 12 issues a write request to one of the front-end directors 20 ₄-20 ₁₁ to perform a write command. One of the front-end directors 20 ₄-20 ₁₁ replies to the request and asks the host computer 12 for the data. After the request has passed to the requesting one of the front-end directors 20 ₄-20 ₁₁, the director determines the size of the data and reserves space in the cache memory 18 to store the request. The front-end director then produces control signals on either a high address memory bus (TH or BH) or a low memory address bus (TL, BL) connected to such front-end director depending on the location in the cache memory 18 allocated to store the data and enable the transfer to the cache memory 18. The host computer 12 then transfers the data to the front-end director. The front-end director then advises the host computer 12 that the transfer is complete. The front-end director looks up in a Table, not shown, stored in the cache memory 18 to determine which one of the rear-end directors 20 ₀-20 ₃ and 20 ₁₂-20 ₁₅ is to handle this request. The Table maps the host computer 12 address into an address in the bank 14 of disk drives. The front-end director then puts a notification in a “mail box” (not shown and stored in the cache memory 18) for the rear-end director which is to handle the request, the amount of the data and the disk address for the data. Other rear-end directors poll the cache memory 18 when they are idle to check their “mail boxes”. If the polled “mail box” indicates a transfer is to be made, the rear-end director processes the request, addresses the disk drive in the bank, reads the data from the cache memory and writes it into the addresses of a disk drive in the bank 14. When data is to be read from the disk drive to the host computer 12 the system operates in a reciprocal manner.

Each one of the rear-end portion of the directors 20 ₀-20 ₃ is identical in construction and are described in detail in the above-referenced co-pending patent application Ser. No. 09/224,194 to include a pair of central processing sections, CPU X and CPU Y, a dual port random access memory (RAM), and shared resources (Flash memories, etc,) coupled to the bank 14 of disk drives (FIG. 1) through the fibre channel (FC) port by-pass sections (FIG. 3), as indicated and to a high memory address bus, here TH, and low memory address bus, here BL. It should be noted that the director 20 ₀-20 ₃ and 20 ₁₂-20 ₁₅ has a first output port, A, and a second output port, B. Further, it should be noted that different pairs of the rear-end directors 20 ₀, 20 ₁; 20 ₂, 20 ₃; 20 ₁₂, 20 ₁₃ (not shown); and, 20 ₁₄, 20 ₁₅ are arranged in redundant fibre channel (FC) networks 25 ₁-25 ₄, respectively, as indicated. Still further, it is noted that each one of the redundant fibre channel (FC) networks 25 ₁-25 ₄ also includes pairs of the fibre channel (FC) port by-pass sections 23 ₁, 23 ₂; 23 ₃, 23 ₄; 23 ₅ (not shown), 23 ₆ (not shown); and, 23 ₇, 23 ₈, respectively, as indicated and disk drive sets 14 ₁, 14 ₂; 14 ₃, 14 ₄; 14 ₅ (not shown), 14 ₆ (not shown); and, 14 ₇, 14 ₈, respectively, as indicated. Each one of the pairs of the redundant fibre channel (FC) networks 25 ₁-25 ₄ is identical in construction, an exemplary one thereof, here redundant fibre channel (FC) networks 25 ₁ is shown in detail in FIG. 2.

Thus, as shown in FIG. 2, the first port A and second port B of director 20 ₀ is connected to both FC port by-pass section 23 ₁ and to FC port by-pass section 23 ₂. Likewise, the first port A and second port B of director 20 ₁ is connected to both FC port by-pass section 23 ₁ and to FC port by-pass section 23 ₂. More particularly, both directors 20 ₀ and 20 ₁ of the redundant FC network 25 ₁ are connected to the pair of FC port by-pass sections 23 ₁, 23 ₂. Each one of the FC port by-pass sections 23 ₁, 23 ₂ includes a pair of FC port by-passes 34 _(A) and 34 _(B). Each one of the FC port by-passes 34 _(A) and 34 _(B) is connected to a corresponding one of a plurality of sets 14 ₁, 14 ₂ of the disk drives in the bank of disk drives 14 (FIG. 1). Each one of the FC port by-passes 34 _(A), 34 _(B) and is identical in construction, an exemplary one thereof, here FC port by-pass 34 _(A) being shown in detail in FIG. 3 connected to set 14 ₁ of the disk drives and to directors 20 ₀ and 20 ₁. It is noted that director 20 ₀ is connected to busses TH and BL and that director 20 ₁ is connected to busses TL and BH. Thus, the redundant FC network 25 ₁ (FIG. 1) is connected to all four busses TH, BH, TL, and BL.

More particularly, and referring again also to FIG. 2, it is noted that each one of the disk drive sets 14 ₁, 14 ₂ includes a plurality of, here for example eight, disk drives 19 ₁-19 ₈, it being understood that the number of disk drives 19 in a set can be selected in accordance with the requisite storage requirements. It is also noted that each one of the disk drives 19 ₁-19 ₈ includes a pair of input/output ports A, B. As noted above, each one of the FC port by-pass sections 23 ₁-23 ₈ is identical in construction. An exemplary one thereof, here FC port by-pass section 23 ₁ is shown in FIG. 2 to include: an input/output port 30A coupled to the A port of director 20 ₀ and a plurality of, here in this example, eight, output/input ports 32 _(A1)-32 _(A8) serially connected between a first one of the ports, here port A, of the plurality of disk drives 19 ₁-19 ₈ through a plurality of fibre channel links 29 _(A1)-29 _(A8). The fibre channel port by-pass selector section 23 ₁ is adapted to couple port A of director 20, serially to a selected one, or ones, of port A of the plurality of disk drives 19 ₁-19 ₈ in set 14 ₁ through a first fibre channel comprising one, or more, of the plurality of fibre channel links 29 _(A1)-29 _(A8) during a normal mode of operation. The fibre channel port by-pass selector section 23 ₁ also has an input/output port 30 _(B) coupled to the A port of director 20, and a plurality of output/ports 32 _(B1)-32 _(B8) serially connected between the B ports of the plurality of disk drives 19 ₁-19 ₈ through fibre channel links 29 _(B1)-29 _(B8), as indicated. The fibre channel port by-pass selector section 23 ₁ is adapted to couple the A port of director 20 ₁ serially to a selected one, or ones, of the B ports of the plurality of disk drives 19 ₁-19 ₈ in set 14 ₁ through a second fibre channel comprising one, or more, of the second plurality of fibre channel links 29 _(B1)-29 _(B8) in the normal operating mode.

Likewise, fibre channel port by-pass selector section 23 ₂ in FIG. 2 is shown to includes: an input/output port 30 _(A) coupled here, however, coupled to the B port of director 20 ₀ and a plurality of, here in this example, eight, output/input ports 32 _(A1)-32 _(A8) serially connected between port A of the plurality of disk drives 19 ₁-19 ₈ in set 14 ₂ through a plurality of fibre channel links 29 _(A1)-29 _(A8). The fibre channel port by-pass selector section 23 ₂ is adapted to couple port B of director 20 ₀ serially to a selected one, or ones, of port A of the plurality of disk drives 19 ₁-19 ₈ in set 14 ₂ through a first fibre channel comprising one, or more, of the plurality of fibre channel links 29 _(A1)-29 _(A8) in section 23 ₂ during a normal node of operation. The fibre channel port by-pass selector section 23 ₂ also has an input/output port 30 _(B) coupled to the B port of director 20 ₁ and a plurality of output/ports 32 _(B1)-32 _(B8) serially connected between the B ports of the plurality of disk drives 19 ₁-19 ₈ in set 14 ₂ through fibre channel links 29 _(B1)-29 _(B8), as indicated. The fibre channel port by-pass selector section 23 ₂ is adapted to couple the B port of director 20 ₁ serially to a selected one, or ones, of the B ports of the plurality of disk drives 19 ₁-19 ₈ in set 14 ₂ through a second fibre channel comprising one, or more, of the second plurality of fibre channel links 29 _(B1)-29 _(B8) in section 23 ₂ in the normal operating mode.

It is noted that director 20 ₀ is able to access the disk drives 19 ₁-19 ₈ in set 14 ₂ through its port B in the event of a failure in director 20 ₁ and, likewise, director 20 ₁ is able to access disk drives 19 ₁-19 ₈ in set 14 ₁ through its A port in the event of a failure in director 20 ₀.

It is also noted that in the event of a failure of, or removal of, any one of the port A or port B by-passes 34A, 34B, both sets of disk drives 14 ₁ and 14 ₂ are still accessible from one of the directors 20 ₀ and 20 ₁. For example, if the port A by-pass 34A of fibre channel port by-pass section 23 ₁ fails or is removed, the set 14 ₁ of disk drives is accessible from director 20 ₁, via the path between port A of director 20 ₁, the port B by-pass 34B of fibre channel by-pass section 23 ₁, and the port B of the disk drives in set 14 ₁. In like manner, if the port B by-pass 34B of fibre channel port by-pass section 23 ₁ fails or is removed, the set 14 ₁ of disk drives is accessible from director 20 ₁, via the path between port A of director 20 ₀, the port A by-pass 34A of fibre channel by-pass section 23 ₁, and the port A of the disk drives in set 14 ₁. If the port A by-pass 34A of fibre channel port by-pass section 23 ₂ fails or is removed, the set 14 ₂ of disk drives is accessible from director 20 ₀, via the path between port B of director 20 ₁, the port B by-pass 34B of fibre channel by-pass section 23 ₁, and the port B of the disk drives in set 14 ₂. In like manner, if the port B by-pass 34B of fibre channel port by-pass section 23 ₂ fails or is removed, the set 14 ₂ of disk drives is accessible from director 20 ₀, via the path between port B of director 20 ₀, the port A by-pass 34A of fibre channel by-pass section 23 ₂, and the port A of the disk drives in set 14 ₂.

Referring now to FIG. 3, an exemplary one of the FC port by-pass sections 23 ₁-23 ₈, here section 23 ₁ is shown in detail connected to set 14 ₁ of disk drives 19 ₁-19 ₈ and to ports A of directors 20 ₀ and 20 ₁. As shown also in FIG. 2, the FC port by-pass section 23 ₁ includes a pair of FC port by-passes 34 _(A), 34 _(B). The FC port by-pass 34 _(A) is coupled between input/output port 30 _(A) and the A ports of the disk drives 19 ₁-19 ₈ in set 14 ₁ through fibre channel links 29 _(A1)-29 _(A8) and the FC port by-pass 34 _(B) is coupled between input/output port 30 _(B) and the B ports of the disk drives 19 ₁-19 ₈ in set 14 ₁ through fibre channel links 29 _(B1)-29 _(B8).

Referring again to FIG. 3, the FC port by-pass 34 _(A) includes selectors 36 _(A1)-36 _(A12) and a control section 40 _(A). (It should be understood that the number of selectors is determined in accordance with the requisite storage requirements). Each one of the selectors 36 _(A1)-36 _(A12) has a pair of input ports (i.e., an A input and a B input) and an output port, one of the input ports A or B being coupled to the output port selectively in accordance with a control signal C_(A1)-C_(A12), respectively, fed thereto, as indicated, by the control section 40 _(A) It is also noted that input/output port 30 _(A) has an input port 30 _(AI), and an output port 30 _(AO).

It is noted that the selectors 36 _(A1)-36 _(A5); and, 36 _(A8)-36 _(A11) are arranged in two selector sections 37 _(A1) and 37 _(A2). Section 37 _(A1) is coupled to disk drives 19 ₁-19 ₄ and section 37 _(A2) is coupled to disk drives 19 ₅-19 ₈. Each section 37 _(A1), 37 _(A2) is used to control whether one, or more, of the disk drives coupled thereto should be by-passed. In like manner. the selectors 36 _(B1)-36 _(B5); and, 36 _(B8)-36 _(B11) are arranged in two selector sections 37 _(B1) and 37 _(B2) Section 37 _(B1) is coupled to disk drives 19 ₁-19 ₄ and section 37 _(B2) is coupled to disk drives 19 ₅-19 ₈. Each section 37 _(B1), 37 _(B2) is used to control whether one, or more, of the disk drives 19 ₁-19 ₄, 19 ₅-19 ₈ coupled thereto, respectively, should be by-passed.

Selector 36 _(A1) has its A input connected to input port 30 _(AI) and its B input port connected to output port 30 _(AO). The outputs of selectors 36 _(A1)-36 _(A11) are connected to the B inputs of selectors 36 _(A2)-36 _(A12) respectively. The outputs of selectors 36 _(A1)-36 _(A4) and 36 _(A7)-36 _(A10) are also coupled to the A ports of disk drives 19 ₁-19 ₈, respectively as shown. The output of selector 36 _(A12) is connected to the A input of selector 36 _(A6). The output of selector 36 _(A6) is connected to both the B input of selector 36 _(A1) and the input port 30 _(AI) of director 20 ₀, as indicated. The output of selector 36 _(A12) is also connected to the A input of selector 36 _(A7). The A inputs of selectors 36 _(A2)-36 _(A5) and 36 _(A8)-36 _(A11) are fed thereto from the A ports of disk drives 19 ₁-19 ₈, respectively, as indicated. It is noted that the output of selector 36 _(A11), in addition to being fed to the B input of selector 36 _(A12) is connected to an expansion port 30 _(EXAO) and that the A input of selector 36 _(A12) is connected to an expansion port 30 _(EXAI), for reasons to be discussed in more detail below in connection with FIGS. 4, 4A and 4B.

The FC port by-pass 34 _(B) includes selectors 36 _(B1)-36 _(B12) and a control section 40 _(B). Each one of the selectors 36 _(B1)-36 _(B12) has a pair of input ports (i.e., an A input and a B input) and an output port, one of the input ports A or B being coupled to the output port selectively in accordance with a control signal C_(B1)-C_(B12), respectively, fed thereto, as indicated, by the control section 40 _(B). It is also noted that input/output port 30 _(B) has an input port 30 _(BI) and an output port 30 _(BO).

It is noted that the selectors 36 _(B1)-36 _(B5); and, 36 _(B8)-36 _(B11) are arranged in two selector sections 37 _(B1) and 37 _(B2). Section 37 _(B1) is coupled to disk drives 19 ₁-19 ₄ and section 37 _(B2) is coupled to disk drives 19 ₅-19 ₈. Each section 37 _(B1), 37 _(B2) is used to control whether one, or more, of the disk drives coupled thereto should be by-passed. In like manner. the selectors 36 _(A1)-36 _(B5); and, 36 _(A8)-36 _(A11) are arranged in two selector sections 37 _(A1) and 37 _(A2). Each section 37 _(B1), 37 _(B2) is used to control whether one, or more, of the disk drives 19 ₁-19 ₄, 19 ₅-19 ₈ coupled thereto, respectively, should be by-passed. Selector 36 _(B1) has its A input connected to input port 30 _(B1) and its B input port connected to output port 30 _(BO). The outputs of selectors 36 _(B1)-36 _(B11) are connected to the B inputs of selectors 36 _(B2)-36 _(B12), respectively. The outputs of selectors 36 _(B1)-36 _(B4) and 36 _(B7)-36 _(B10) are also coupled to the B ports of disk drives 19 ₁-19 ₈, respectively as shown. The output of selector 36 _(B12) is connected to the A input of selector 36 _(B6). The output of selector 36 _(B6) is connected to both the B input of selector 36 _(B1) and the input port 30 _(BI) of director 20 ₁, as indicated. The output of selector 36 _(B12) is also connected to the A input of selector 36 _(B7). The A inputs of selectors 36 _(B2)-36 _(B5) and 36 _(B8)-36 _(B11) are fed thereto from the B ports of disk drives 19 ₁-19 ₈, respectively, as indicated. It is noted that the output of selector 36 _(B12), in addition to being fed to the B input of selector 36 _(B12) is connected to an expansion port 30 _(EXBO) and that the A input of selector 36 _(B12) is connected to an expansion port 30 _(EXBI), for reasons to be discussed in more detail below in connection with FIGS. 4, 4A and 4B.

NORMAL OPERATING MODE

During the normal operating mode, port 30 _(A) of director 20 ₀ is coupled serially through disk drives 19 ₁-19 ₄ of set 14 ₁ via ports A of such disk drives 19 ₁-19 ₄ and port 30 _(B) of director 20 ₁ is coupled serially through disk drives 19 ₅-19 ₈ of set 14 ₁ via ports B of such disk drives 19 ₅-19 ₈. Such is accomplished by the control signals C_(A1)-C_(A12) and C_(B1)-C_(B12) which couple one of the A and B ports of the selectors coupled to the outputs of such selectors in the following TABLE:

SELECTOR INPUT PORT COUPLED TO SELECTOR OUTPUT 36_(A1) A 36_(A2) A 36_(A3) A 36_(A4) A 36_(A5) A 36_(A6) A 36_(A7) B 36_(A8) B 36_(A9) B 36_(A10) B 36_(A11) B 36_(A12) B 36_(B1) A 36_(B2) B 36_(B3) B 36₆₄ B 36_(B5) B 36_(B6) A 36_(B7) B 36_(B8) A 36_(B9) A 36_(B10) A 36_(B11) A 36_(B12) B

In the event of a failure in one of the disk drives 19 ₁-19 ₈, the control sections 40A and 40B are advised of such failure by the directors 20 ₀ and 20 ₁ via control lines 45 ₀, 45 ₁, respectively. For example, assume there is a failure in disk drive 19 ₃. Once such a failure is detected during the normal operating mode, control section 40A changes the logic state on control line C_(A4) to thereby de-couple input port A of selector 36 _(A4) from its output and couples input port B of selector 36 _(A4) to its output; thereby by-passing disk drive 19 ₃ from the first fibre channel (i.e., the fibre channel through the input and output ports 30 _(AI) and 30 _(AO) of director 20 ₀). In like manner, if there is a failure in disk drive 19 ₇, once such a failure is detected during the normal operating mode, control section 40 _(B) changes the logic state on control line CB_(A10) to thereby de-couple input port A of selector 36 _(B10) from its output and couples input port B of selector 36 _(B10) to its output; thereby by-passing disk drive 19 ₇ from the second fibre channel (i.e., the fibre channel through the input and output ports 30 _(BI) and 30 _(BO) of director 20 ₁).

FAILURE OF ONE OF THE DIRECTORS 20 ₀ or 20 ₁

As noted above, during normal operation, director 20 ₀ is coupled to the A ports of disk drives 19 ₁-19 ₄ and director 20 ₁ is coupled to the B ports of disk drives 19 ₅-19 ₈. In the event of a failure in director 20 ₀, director 20 ₀ is de-coupled from disk drives 19 ₁-19 ₄ and director 20 ₁ is coupled to the B ports of disk drives 19 ₁-19 ₄ in addition to remaining coupled to the B ports of disk drives 19 ₅-19 ₈. Likewise, in the event of a failure in director 20 ₁, director 20 ₁ is de-coupled from disk drives 19 ₅-19 ₈ and director 20 ₀ is coupled to the A ports of disk drives 19 ₅-19 ₈ in addition to remaining coupled to the A ports of disk drives 19 ₁-19 ₄. Such is accomplished (i.e., removal of failed director 20 ₀, for example) by the control signals C_(A1)-C_(A12) and C_(B1)-C_(B12) which couple one of the A and B ports of the selectors coupled to the outputs of such selectors in the following TABLE:

SELECTOR INPUT PORT COUPLED TO SELECTOR OUTPUT 36_(A1) A 36_(A2) A 36_(A3) A 36_(A4) A 36_(A5) A 36_(A6) A 36_(A7) B 36_(A8) A 36_(A9) A 36_(A10) A 36_(A11) A 36_(A12) B 36_(B1) B 36_(B2) B 36_(B3) B 36₆₄ B 36_(B5) B 36_(B6) A 36_(B7) B 36_(B8) B 36_(B9) B 36_(B10) B 36_(B11) B 36_(B12) B

EXPANSION MODE

As described above in connection with FIG. 1, for each redundant FC network 25 ₁-25 ₄ the A port of one of the rear-end directors thereof is coupled in the normal mode to one disk drive set and the A port of the other one of the rear-end directors thereof is coupled such set of disk drives. Thus, for example, considering redundant FC network 25 ₁ shown more clearly in FIG. 2, during the normal operating mode, the A port of rear-end director 20 ₀ and the A port of rear-end director 20 ₁ are coupled to disk drive set 14 ₁ through port by-passes 34 _(A) and 34 _(B), respectively, of port by-pass section 23 ₁. Each one of the rear-end directors 20 ₀-20 ₁₅ (FIG. 1) may, however, may be coupled to more than one disk drive set through the use of additional port by-passes. For example, referring to FIG. 4 and considering port A of the rear-end directors 20 ₀ and 20 ₁, an additional disk drive set 14′₁ is shown coupled to the A ports of rear-end directors 20 ₀ and 20 ₁ through FC port by-passes 34′_(A) and 34′_(B), respectively, as shown. It is first noted that the additional FC port by-passes 34′_(A) and 34′_(B) are identical in construction to FC port by-passes 34 _(A) and 34 _(B) shown in FIG. 3. Thus, referring also to FIGS. 4 and 4A, the same numerical designation is used for the elements in FC port by-pass 34′_(A) as was used in FC port by-pass 34 _(A) except that the elements in FC port by-pass 34′_(A) have a prime (′) numerical designation. It is next noted in FIG. 4, that the A port of director 20 ₀ is connected to the A ports of the disk drives 19 ₁-19 ₈, 19′₁-19′₈ in both disk drive sets 14 ₁ and 14′₁ through FC port by-passes 34 _(A) and 34′_(A), respectively, and that the A port of director 20 ₁ is connected to the B ports of the disk drives 19 ₁-19 ₈ and 19′₁-19′₈, respectively, in both disk drive sets 14 ₁ and 14′₁, respectively, through FC port by-passes 34 _(B) and 34′_(B), respectively. More specifically, and referring also to FIG. 4A, the output of port A of director 20 ₁ is coupled to port 30 _(AI) of FC port by-pass 34 _(A) and the input of port A of director 20 ₀ is coupled to port 30 _(AO). The output of selector 36 _(A6) is coupled to the B input of selector 36 _(A1) of port A by-pass 34 _(A), and to port 30 _(AO). Port 30 _(AI) is coupled to the A input of selector 36 _(A1) of the port A by-pass 34 _(A). The details of the port A by-pass have been described above in connection with FIG. 3. The output of selector 36 _(A11) is connected, through expansion port 30 _(EXAO) to A input of selector 36′_(A1) of port A by-pass 34′_(A) and the output of selector 36′_(A6) of selector 34′_(A) is connected to the B input of selector 36′_(A1) and through port 30′_(AO), to the A input of selector 36 _(A12) of port A by-pass 34 _(A). Thus, port A by-pass 34 _(A) is adapted to service disk drive set 14 and, if expansion is desired, the additional port A by-pass 34′_(A) is adapted to service the additional disk drive set 14′₁.

Referring now also to FIG. 4B, the port A by-pass 34 _(A) and the additional port A by-pass 34′_(A) are shown in more detail. Thus, the FC port by-pass 34 _(A) includes selectors 36 _(A1)-36 _(A12) and a control section 40 _(A). Each one of the selectors 36 _(A1)-36 _(A12) has a pair of input ports (i.e., an A input and a B input) and an output port, one of the input ports A or B being coupled to the output port selectively in accordance with a control signal C_(A1-C) _(A12), respectively, fed thereto, as indicated, by the control section 40 _(A). It is also noted that input port 30 _(AI) is coupled to port A of director 20 ₀ and the output of selector 36 _(A6) of by-pass 34 _(A) is coupled to port 30 _(AO), as in FIG. 4A.

During the normal mode of operation, port 30 _(A) of director 20 ₀ is coupled serially through disk drives 19 ₁-19 ₄ of set 14 ₁ via ports A of such disk drives 19 ₁-19 ₄ and through disk drives 19′₁-19′₄ and then back to port 30′_(AO). Such is accomplished by the control signals C_(A1)-C_(A12) and C′_(A1)-C′_(A12) which couple one of the A and B ports of the selectors coupled to the outputs of such selectors in the following TABLE:

SELECTOR INPUT PORT COUPLED TO SELECTOR OUTPUT 36_(A1) A 36_(A2) A 36_(A3) A 36_(A4) A 36_(A5) A 36_(A6) A 36_(A7) B 36_(A8) B 36_(A9) B 36_(A10) B 36_(A11) B 36_(A12) A 36′_(A1) A 36′_(A2) A 36′_(A3) A 36′_(A4) A 36′_(A5) A 36′_(A6) B 36′_(A7) B 36′_(A8) B 36′_(A9) B 36′_(A10) B 36′_(A11) B 36′_(A12) B

In the event of a failure in director 20 ₁, director 20 ₀ is coupled to the A ports of disk drives 19′₁-19′₈ and 19 ₁-19 ₈. Such is accomplished by the control signals C_(A1)-C_(A12) and C′_(A1)-C′_(A12) which couple one of the A and B ports of the selectors coupled to the outputs of such selectors in the following TABLE:

SELECTOR INPUT PORT COUPLED TO SELECTOR OUTPUT 36′_(A1) A 36_(A2) A 36_(A3) A 36_(A4) A 36_(A5) A 36_(A6) A 36_(A7) B 36_(A8) A 36_(A9) A 36_(A10) A 36_(A11) A 36_(A12) A 36′_(A1) A 36′_(A2) A 36′_(A3) A 36′_(A4) A 36′_(A5) A 36′_(A6) A 36′_(A7) B 36′_(A8) A 36′_(A9) A 36′_(A10) A 36′_(A11) A 36′_(A12) B

It is understood that appropriate control signals are produced by FC port by-passes 34 _(B), 34′_(B) (FIGS. 4. 4A and 4B) to de-couple failed director 20 ₁ from the B ports of disk drives 19 ₄-19 ₈ and 19′₄-19′₈.

CONTRACTION MODE

Referring now to FIGS. 5, and 5A, an arrangement is shown where the disk drive set 14 ₁ in bank 14 (FIG. 1) has 24 disk drives 19″₁-19″₂₄ instead of the 8 disk drive set 14 ₁-14 ₈ discussed above. Further, a redundant FC network 25″₁ includes, in addition to the rear-end directors 20 ₀ and 20 ₁ described above in connection with redundant FC network 25 ₁ (FIG. 1), a pair of additional rear-end directors 20″₀ and 20″₁. Director 20″₁ is coupled to busses TL and BH (FIG. 1) and director 20″₁, is coupled to busses TH and BL (FIG. 1). The A port of director 20″₀ is coupled to the A ports of the disk drives 19″₁-19″₂₄ in disk drive set 14″₁ through port A by-pass 34″_(A) of port by-pass section 23″₁ and the B port of director 20″₀ is coupled to the A ports of the disk drives 19″₁-19″₂₄ in disk drive set 14″₂ through port A by-pass 34′_(A) of port by-pass section 23″₂. The A port of director 20″₁, is coupled to the B ports of the disk drives 19″₁-19″₂₄ in disk drive set 14″₁ through port B by-pass 34″_(A) of port by-pass section 23″₁ and the B port of director 20″₁ is coupled to the B ports of the disk drives 19″₁-19″₂₄ in disk drive set 14″₂ through port B by-pass 34″_(B) of port by-pass section 23″₂. In a manner similar to the redundant FC network 25 ₁ described above in connection with FIGS. 1 and 2, the A port of director 20 ₀ is coupled to the A ports of the disk drives 19″₁-19″₂₄ in disk drive set 14″₁ through port A by-pass 34-_(A) of port by-pass section 23″₁, and the B port of director 20 ₀ is coupled to the A ports of the disk drives 19″₁-19″₂₄ in disk drive set 14″₂ through port A by-pass 34″_(A) of port by-pass section 23″₂. Likewise, the A port of director 20 ₁ is coupled to the B ports of the disk drives 19″₁-19″₂₄ in disk drive set 14″₁ through port A by-pass 34″_(A) of port by-pass section 23″₁ and the B port of director 20 ₁ is coupled to the B ports of the disk drives 19″₁-19″₂₄ in disk drive set 14″₂ through port B by-pass 34″_(B) of port by-pass section 23″₂.

Thus, here each set of disk drives 14″₁ and 14″₂ may be coupled to four rear-end directors 20 ₀, 20 ₁, 20″₀, 20″₁. The connections of rear-end directors 20 ₀ and 20 ₁ is at the input/output ports 30″_(A), 30″_(B) of the port A by-passes 34″_(A), 34″_(B) of port by-pass sections 23″₁ and 23″₂, respectively, in a manner similar to that described above in connection with FIG. 2. The connections of rear-end directors 20″₀ and 20″₁ is at the expansion input/output ports 30″_(EXA), 30″_(EXB) of the port A by-passes 34″_(A), 34″_(B) of port by-pass sections 23″₁ and 23″₂, respectively, as shown more clearly in FIGS. 5A and 5B.

It is first noted that each of the port A and port B by-passes 34″A and 34″_(B) is identical in construction. An exemplary one thereof, here port B by-pass 34″_(B) is shown in detail in FIGS. 5B and 5C. More particularly, and referring to FIGS. 5B and 5C, the disk drives 19″₁-19″₂₄ are arranged in four sets, each set being coupled to a corresponding one of four selector sections 37″₁-37″₄, as indicated. Thus, disk drives 19″₇-19″₁₂ are coupled to selector section 37″₁, disk drives 19″₁-19″₆ are coupled to selector section 37″₂, disk drives 19″₁₉-19″₂₄ are coupled to selector section 37″₃, and disk drives 19″₁₃-19″₁₈ are coupled to selector section 37″₄, as indicated. The selectors: 36″_(B2)-36″_(B7); 36″_(B9)-36″_(B14); 36″_(B17)-36″_(B22); and, 36″₂₅-36″_(B30), in the sections 37″₁; 37″₂; 37″₃; and 37″₄, respectively, are controlled by control signals fed to the selectors therein by control 40″_(B) in a manner similar to that described above in FIG. 3 in connection with controls 40 _(A) and 40 _(B). Referring also to FIG. 5C, the port B by-pass 34″ is shown to include, in addition to the selectors in the four selectors sections 37″₁-37″₄, described above in connection with FIG. 5B, selectors 36″_(B1), 36″_(B8), 36″_(B15), 36″₁₆, 36″₂₃, 36″_(B24), 36″_(B31), and 36″_(B32), arranged as shown.

Referring again also to FIGS. 5 and 5A, and the exemplary port B by-pass 34″_(B), it is noted that port A of rear-end director 20 ₁ is connected to ports 30 _(BI) and 30″_(BO) of input/output port 30″_(B) and that port A of rear-end director 20″₁ is connected to ports 30 _(EXI) and 30″_(EXO) of expansion port 30″_(EXB). This arrangement is useful where one has a system with 24 disk dives in each set and then wants to reduce the number of disk drives to either 18, or 12, or 6 disk drives.

More particularly, and referring also to FIG. 5D, rear-end director 20 ₁ a configurations is shown where director 20 ₁ is coupled to the B ports of all 24 disk drives 19″₁-19″₂₄ in set 14″₁ and director 20″₁ is not coupled to any of the 24 disk drives 19″₁-19″₂₄ in set 14″₁. Thus, the output of selector 36″_(B1) is coupled to its input port A (as indicated by the arrows 50), the output of selector 36″_(B8) is coupled to its A input port, the output of selector 36″_(B15) is coupled to its A port, the output of selector 36″₁₆ is coupled to its B port, the output of selector 36″₂₃ is coupled to its A port, the output of selector 36″_(B24) is coupled to its B port, the output of selector 36″_(B31) is coupled to its B port, and the output of selector 36″_(B32) is coupled to its A port.

Thus, the A port of director 20 ₁ connected to the port 30″_(BI) passes through selector 36″_(B1) to the input of selector section 37″₁. The output of selector section 37″₁ then passes successively through: the selector 36″_(B8); selector section 37″₂; selector 36″_(B16); selector section 37″₃; selector 36″_(B24); selector section 37″₄; selector 36″_(B31); selector 36″_(B23); selector 36″_(B15); selector 36″_(B32) then to port 30″_(BO) and back to the A port of director 20 ₁. It is noted that director 20″₁ is by-passed and not connected to the selector sections 37″₁-37″₂ and hence not connectable to the disk drives connected to such selector sections 37″₁-37″₂

If the user wishes to reduce the number of disk drives coupled to director 20 ₁ from 24 to 18 with director 20″₁ coupled to the other 6 disk drives, such a configuration is shown in FIG. 5E. Thus, the output of selector 36″_(B1) remains coupled to its input port A (as indicated by the arrows 50), the output of selector 36″_(B8) remains coupled to its A input port, the output of selector 36″_(B15) remains coupled to its A port, the output of selector 36″₁₆ remains coupled to its B port, the output of selector 36″₂₃ switches to its B port, the output of selector 36″_(B24) switches to its A port, the output of selector 36″_(B31) switches to its A port, and the output of selector 36″_(B32) remains coupled to its A port.

Thus, the A port of director 20 ₁ coupled to port 30″_(BI) is then coupled through selector 36″_(B1) to the input of selector section 37″₁. The output of selector section 37″₁ then passes successively through: the selector 36″_(B8); selector section 37″₂; selector 36″_(B16); selector section 37″₃; selector 36″_(B23); selector 36″_(B15); selector 36″_(B32) and then to port 30″_(BO) and back to the A port of director 20 ₁. The A port of director 20″₁ is connected through selector 36″_(B31) and through selector 36″_(B24) to selector section 37″₄ and the back to the A port of selector 20″₁.

If the user wishes to reduce the number of disk drives coupled to director 20″₁ from 18 to 12 with the director 20″₁ being coupled to the other 12 disk drives, such a configuration is shown in FIG. 5F. Thus, the output of selector 36″_(B1) remains coupled to its input port A (as indicated by the arrows 50), the output of selector 36″_(B8) remains coupled to its A port, the output of selector 36″_(B15) switches to its B port, the output of selector 36″₁₆ switches to its A port, the output of selector 36″₂₃ switches to its A port, the output of selector 36″_(B24) switches to its B port, the output of selector 36″_(B31) remains at its A port, and the output of selector 36″_(B32) remains at its B port.

Thus, the A port of director 20 ₁ coupled to port 30″_(BI) is coupled through selector 36″_(B1) to the input of selector section 37″₁. The output of selector section 37″₁ then passes successively through: the selector 36″_(B8); selector section 37″₂; selector 36″_(B15); selector 36″_(B32) and then to port 30″_(BO) and back to the A port of director 20 ₁. The A port of director 20″₁, connected through selector 36″_(B31) is coupled through selector 36″_(B31) then through selector 36″_(B23); selector 36 _(B16); selector section 37″₃, then through selector 36″_(B24), selector section 37″₄ and the back to the A port of selector 20″₁.

If the user wishes to reduce the number of disk drives coupled to director 20 ₁ from 12 to 6 with the director 20″₁ being coupled to the other 18 disk drives, such a configuration is shown in FIG. 5G. Thus, the output of selector 36″_(B1) remains coupled to its input port A (as indicated by the arrows 50), the output of selector 36″_(B8) is switched to its B port, the output of selector 36″_(B15) is switched to its B port, the output of selector 36″₁₆ is switched to its B port, the output of selector 36″₂₃ remains at its A port, the output of selector 36″_(B24) remains at its B port, the output of selector 36″_(B31) remains at its A port, and the output of selector 36″_(B32) is switched to its A port.

Thus, the A port of director 20 ₁ coupled to port 30″_(BI) is coupled through selector 36″_(B1) to the input of selector section 37″₁. The output of selector section 37″₁ then passes through selector 36″_(B32) and then to port 30″_(BO) and back to the A port of director 20 ₁. The A port of director 20″₁. connected through selector 36″_(B31) is coupled through selector 36″_(B31) then through successively through selector 36″_(B23); selector 36 _(B15), selector section 37 ₂, selector 36 _(B16), selector section 37″₃, selector 36 _(B24), to selector section 37″₃, then through selector 36″_(B24) to selector section 37″₄ and the back to the A port of selector 20″₁.

Other embodiments are within the spirit and scope of the appended claims. 

What is claimed is:
 1. A data storage system, comprising: (a) a set of disk drives, each one of the disk drives thereof having a pair of bi-directional ports; (b) a host computer; (c) an interface for coupling data between the host computer and the set of disk drives through the interface, such interface comprising: (i) a plurality of buses; (ii) a redundant fibre channel network coupled between the plurality of buses and the set of disk drives, such network comprising: (A) a pair of directors for controlling flow of data to and from the disk drives through a first and a second fibre channel, respectively; (B) a first fibre channel port by-pass, comprising: (1) a bi-directional input/output port coupled to a first one of the directors; (2) a plurality of bi-directional output/input ports, each one being connected to a first one of the pair of bi-directional ports of a corresponding one of the disk drives in the set of disk drives through a first plurality of fibre channel links; and (3) wherein the first fibre channel port by-pass is adapted to couple the first one of the directors serially to one, or ones, of the plurality of disk drives in the set thereof through the first fibre channel selectively in accordance with a control signal, such first fibre channel comprising one, or more, of the first plurality of fibre channel links; and (C) a second fibre channel port by-pass, comprising: (1) a bi-directional input/output port coupled to a second one of the directors; (2) a plurality of bi-directional output/input ports, each one being connected between a second one of the pair of bi-directional ports of a corresponding one of the disk drives in the set of disk drives through a second plurality of fibre channel links; and (3) wherein the second fibre channel port by-pass selector section is adapted to couple the second one of the directors serially to one, or ones, of the plurality of disk drives in the set thereof through the second fibre channel selectively in accordance with the control signal, such second fibre channel comprising one, or more, of the second plurality of fibre channel links; and wherein the first fibre channel and the second fibre channel provide separate fibre channels to and from the plurality of coupled disk drives and wherein the first and second fibre channel includes the same disk drives in the set thereof.
 2. The system recited in claim 1 including: a second set of disk drives, each one of the disk drives in the second set thereof having a pair of bi-directional ports; a third and a fourth port by-pass; wherein: each one of the pair of directors has a second input/output port; and wherein the third port by-pass includes: a bi-directional input/output port coupled to a second one of the pair of ports of the first one of the pair of directors; and, a plurality of output/input port, each one being connected to a first one of the pair of bidirectional ports of a corresponding one of the disk drives in the second set of disk drives through a third plurality of fibre channel links; wherein the third port by-pass is adapted to couple the second input/output port of a first one of the pair of directors serially to one, or ones, of the plurality of disk drives in the second set thereof through a third fibre channel selectively in accordance with a control signal, such third fibre channel comprising one, or more of the third plurality of fibre channel links; and wherein the fourth port by-pass section includes: an input/output port coupled to the second input/output port of a second one of the pair of directors; and, a plurality of output/input ports, each one being connected to the second one of the pair of bi-directional ports of a corresponding one of the disk dives in the second set of disk drives through a fourth plurality of fibre channel links; and wherein the fourth port by-pass is adapted to couple the second input/output port of the second one of the pair of directors serially to one, or ones, of the plurality of disk drives in the second set thereof through a fourth fibre channel selectively in accordance with a control signal, such fourth fibre channel comprising one, or more of the fourth plurality of fibre channel links; and wherein the first, second, third and fourth fibre channels provide separate fibre channels to and from the plurality of coupled disk drives and wherein the third and fourth fibre channels includes the same disk drives in the second set thereof.
 3. A data storage system, comprising: (a) a set bank of disk drives, each one of the disk drives having a pair of bi-directional ports; (b) a host computer; (c) an interface for coupling data between the host computer and the bank of disk drives through the interface, such interface comprising: (i) a plurality of buses; (ii) a redundant fibre channel network coupled between the plurality of buses and disk drives, such network comprising: (A) a pair of directors for controlling flow of data to and from the disk drives through a first and a second fibre channel, respectively, each one of the directors having a pair of bi-directional ports; (B) a fibre channel port by-pass selector section, comprising: (1) a pair of bidirectional input/output ports coupled to first ones of the pair of ports of the pair of directors; (2) a plurality of bidirectional output/input ports, each one of a first set thereof being connected to a first one of the pair of ports of a corresponding one of the disk drives in the set of the disk drives through a first plurality of fibre channel links and each one of a second set thereof being connected to a second one of the pair of ports of a corresponding one of the disk drives in the set of the disk drives through a second plurality of fibre channel links; and (3) wherein the fibre channel port by-pass selector section is adapted to couple the first one of the directors serially to one, or ones, of the plurality of disk drives in the set thereof through the first fibre channel selectively in accordance with a control signal, such first fibre channel comprising one, or more, of the first plurality of fibre channel links; and wherein the fibre channel port by-pass selector section is adapted to couple the second one of the directors serially to one, or ones, of the plurality of disk drives in the set thereof through the second fibre channel selectively in accordance with the control signal, such second fibre channel comprising one, or more, of the second plurality of fibre channel links and, wherein the first fibre channel and the second fibre channel provide separate fibre channels to and from the plurality of coupled disk drives and wherein the first and second fibre channels include the same disk drives in the set of disk drives.
 4. The system recited in claim 3 wherein: each one of the port by-pass section has a pair of port by-passes, a first one of the port by-passes being connected to a first one of the pair of input/output ports of such port by-pass section and a second one of the port by-passes being connected to a second one of the pair of input/output ports of such port by-pass section; and wherein the first one of the port by-passes is connected to the first one of the pair of ports of the disk drives in the set of disk drives connected thereto and the second one of the port by-passes is connected to a second one of the pair of ports of the set of disk drives connected thereto.
 5. A data storage system, comprising: (a) a plurality of disk drives, each one having of the disk drives in the bank having a pair of bidirectional ports; (b) a host computer; (c) an interface for coupling data between the host computer and the bank of disk drives through the interface, such interface comprising: (i) a plurality of buses; (ii) a redundant fibre channel network coupled between the plurality of buses and disk drives, such network comprising: (A) a pair of directors for controlling flow of data to and from the disk drives through a first and a second fibre channel, respectively; (B) a first fibre channel port by-pass selector section, comprising: (1) a bidirectional input/output port coupled to a first one of the directors; (2) a plurality of bi-directional output/input ports, each one being connected between a first one of the ports of a corresponding one of the plurality of disk drives through a first plurality of fibre channel links; and (3) wherein the first fibre channel port by-pass selector section is adapted to couple the first one of the directors serially to one, or ones, of the first ports of the plurality of disk drives through the first fibre channel selectively in accordance with a control signal, such first fibre channel comprising one, or more, of the first plurality of fibre channel links; and (C) a second fibre channel port by-pass selector section, comprising: (1) a bidirectional input/output port coupled to a second one of the directors; (2) a plurality of bi-directional output/ports, each one being connected between a second one of the pair of ports of a corresponding one of the plurality of disk drives through a second plurality of fibre channel links; and (3) wherein the second fibre channel port by-pass selector section is adapted to couple the second one of the directors serially to one, or ones, of the second ports of the plurality of disk drives through the second fibre channel selectively in accordance with the control signal, such second fibre channel comprising one, or more, of the second plurality of fibre channel links; and wherein the first fibre channel and the second fibre channel provide separate fibre channels to and from the plurality of coupled disk drives and wherein the first and second fibre channels include the same disk drives in the plurality of disk drives.
 6. The system recited in claim 5 wherein: each one of the pair of directors has a pair of bidirectional input/output ports; each one of the first and second port by-pass sections has a pair of bi-directional input/output ports; and wherein a first one of the pair of directors has: a first one of the input/output ports thereof coupled to a first one of the pair of the input/output ports of the first fibre channel port by-pass section; and, a second one of the input/output ports thereof coupled to a first one of the pair of input/output ports of the second fibre channel port by-pass section; and wherein a second one of the pair of directors has: a first one of the output/input ports thereof coupled to a second one of the output/input ports of the first fibre channel port by-pass section; and, a second one of the input/output ports thereof coupled to the second one of the pair of input/output ports of the second fibre channel port by-pass section.
 7. The system recited in claim 6 wherein the first fibre channel port by-pass selector section is coupled to a first set of the plurality of disk drives and the second fibre channel port by-pass selector section is coupled to a different set of the plurality of disk drives.
 8. A data storage system, comprising: (a) a plurality of disk drives, each one having a pair of bidirectional ports; (b) a pair of directors for controlling flow of data to and from the disk drives; (c) a fibre channel port selector section comprising: (i) a plurality of first ports, each one being connected between a first one of the ports of a corresponding one of the plurality of disk drives through a first plurality of fibre channel links; and (ii) a plurality of second ports, each one being connected between a second one of the pair of ports of a corresponding one of the plurality of disk drives through a second plurality of fibre channel links; (iv) a third port coupled to a first one of the pair of directors; (v) a fourth port coupled to a second one of the pair of directors; and (vi) wherein the fibre channel port selector section is adapted to: couple the first one of the directors serially to one, or ones, of the first ports of the plurality of disk drives through a first fibre channel selectively in accordance with a control signal, such first fibre channel comprising one, or more, of the first plurality of fibre channel links; and, couple the second one of the directors serially to one, or ones, of the second ports of the plurality of disk drives through a second fibre channel selectively in accordance with the control signal, such second fibre channel comprising one, or more, of the second plurality of fibre channel links; and wherein the first fibre channel and the second fibre channel provide separate fibre channels tc and from the plurality of coupled disk drives and wherein the first and second fibre channels include the same disk drives in the plurality of disk drives.
 9. A data storage system, comprising: (a) a first and a second set of disk drives, each one of the disk drives having a pair of bi-direcfional ports; (b) a pair of directors for controlling flow of data to and from the disk drives, each one of the directors having a pair of ports; (c) a first fibre channel port by-pass, comprising: an input/output port coupled to a first one of the pair of ports of a first one of the pair of directors; a plurality of output/input ports, each one being connected between a first one of the ports ofa corresponding one of the disk drives of the first set of disk drives through a first plurality of fibre channel links; and wherein the first fibre channel port by-pass selector is adapted to couple the first one of the ports of the first one of the pair of directors serially to one, or ones, of the first ports of the first plurality of disk drives through a first fibre channel selectively in accordance with a control signal, such first fibre channel comprising one, or more, of the first plurality of fibre channel links; and (d) a second fibre channel port by-pass, comprising: an input/output port coupled to a first one of the pair of ports of a second one of the pair of directors; a plurality of output/ports, each one being serially connected between a second one of the pair of ports of a corresponding one the disk drives in the first set pf disk drives through a second plurality of fibre channel links; and wherein the second fibre channel port by-pass selector section is adapted to couple the first one of the pair of ports of the second one of the pair of directors serially to one, or ones, of the second ports of the first plurality of disk drives through a second fibre channel selectively in accordance with the control signal, such second fibre channel comprising one, or more, of the second plurality of fibre channel links; (e) a third fibre channel port by-pass, comprising: an input/output port coupled to a second one of the pair of ports of the first one of the pair of directors; a plurality of output/input ports, each one being serially connected between a first one of the ports of a corresponding one of the disk drives in the second set of disk drives through a third plurality of fibre channel links; and wherein the third fibre channel port by-pass selector is adapted to couple the second one of the ports of the first one of the pair of directors serially to a selected one, or ones, of the third ports of the second set of disk drives through a third fibre channel, such third fibre channel comprising one, or more, of the third plurality of fibre channel links; and (f) a fourth fibre channel port by-pass, comprising: an input/output port coupled to second one of the pair of ports of the second one of the pair of directors; a plurality of output/ports, each one being serially connected between a second one of the pair of ports of a corresponding one of the disk drives in the second set of disk drives through a fourth plurality of fibre channel links; and wherein the fourth fibre channel port by-pass selector section is adapted to couple the second one of the pair of ports of the second one of the pair of directors serially to a selected one, or ones, of the second ports of the second set of disk drives through a fourth fibre channel, such fourth fibre channel comprising one, or more, of the fourth plurality of fibre channel links; and wherein the first, second, third and fourth fibre channels provide separate fibre channels to and from the plurality of coupled disk drives and wherein the first and second fibre channels include the same disk drives in the first set of disk drives and the third and fourth fibre channels include the same disk drives in the second set of disk drives.
 10. A data storage system, comprising: (a) a first and second plurality of disk drives, each one of the disk drives having a pair of bi-directional ports; (b) a pair of directors for controlling flow of data to and from the first and second plurality of disk drives; (c) a first fibre channel port selector section comprising: (i) a plurality of first ports, each one being connected to a first one of the ports of a corresponding one of the first plurality of disk drives through a first plurality of fibre channel links; and (ii) a plurality of second ports, each one being connected to a second one of the pair of ports of a corresponding one of the first plurality of disk drives through a second plurality of fibre channel links; (iv) a third port coupled to a first port of a first one of the pair of directors; (v) a fourth port coupled to a first port of a second one of the pair of directors; and (vi) wherein the first fibre channel port selector section is adapted to: couple the first one of the directors serially to one, or ones, of the first ports of the first plurality of disk drives through a first fibre channel selectively in accordance with a control signal, such first fibre channel comprising one, or more, of the first plurality of fibre channel links; and, couple the second one of the directors serially to one, or ones, of the second ports of the first plurality of disk drives through a second fibre channel selectively in accordance with the control signal, such second fibre channel comprising one, or more, of the second plurality of fibre channel links; (d) a second fibre channel port selector section comprising: (i) a plurality of first ports, each one being connected to a first one of the ports of a corresponding one of the second plurality of disk drives through a third plurality of fibre channel links; and (ii) a plurality of second ports, each one being connected to a second one of the pair of ports of a corresponding one of the second plurality of disk drives through a fourth plurality of fibre channel links; (iv) a third port coupled a second port of the first one of the pair of directors; (v) a fourth port coupled to a second port of the second one of the pair of directors; and (vi) wherein the second fibre channel port selector section is adapted to couple the first one of the directors serially to one, or ones, of the third ports of the second plurality of disk drives through a first fibre channel selectively in accordance with the control signal, such third fibre channel comprising one, or more, of the third plurality of fibre channel links; and, couple the second one of the directors serially to one, or ones, of the second ports of the second plurality of disk drives through a fourth fibre channel, such fourth fibre channel comprising one, or more, of the fourth plurality of fibre channel links; and wherein the first, second, third and fourth fibre channels provide separate fibre channels to and from the plurality of coupled disk drives and wherein the first and second fibre channels include the same disk drives in the first plurality of disk drives and the third and fourth fibre channels include the same disk drives in the second plurality of disk drives. 